Identification of linkages of a galactomannan isolated from seed of Caesalpinia pulcherima

Abstract

A galactomannan, purified by repeated complex formation with copper acetate, was shown to be composed of D-mannose and D-galactose in a molar ratio of 3:1. From methylation experiments, the following partially methylated sugars were identified: 2,3,4,6-tetra- O-methyl- D-mannose, 2,3,4,6-tetra- O-methyl- D-galactose, 2,3,6,-tri- O-methyl- D-mannose, 2,4,6,-tri- O-methyl- D-mannose, 3,4,6-tri- O-methyl- D-mannose, and 2,3-di- O-methyl- D-mannose (molar ratio 1:27:60:4:2:32). Ordinary and sequential (Smith) periodate degradation indicated that the D-galactose units occupied single unit branch points linked (1→6); approximately one in every twenty D-mannose units was resistant to periodate attack; the occurrence of small and equimolar quantities of 2- O-β- D-mannopyranosyl- D-erythritol and O-β- D-mannopyranosyl-(1→3)- O-β- D-mannopyranosyl-(1→2)- D-erythritol indicates a low frequency of isolated (1→3) linkages and consecutive (1→3) linkages. A relatively simple structure may be assigned, based upon the experimental results.